1. Field of the Invention
The present invention relates to a photo-curable resin composition, especially to a liquid photo-curable resin composition suitable as material used in photo-fabricating processes and capable of providing cured products having a high moisture resistance and excellent toughness.
2. Description of the Background Art
In recent years, photo-fabricating processes for forming three-dimensional objects consisting of integrally laminated cured resin layers prepared by repeating a step of forming a cured resin layer by selectively irradiating a liquid photo-curable material with light have been proposed (see Japanese Patent Application Laid-open No. 247515/1985, U.S. Pat. No. 4,575,330 (Japanese Patent Application Laid-open No. 35966/1987), Japanese Patent Application Laid-open No. 101408/1987, Japanese Patent Application Laid-open No. 24119/1993).
A typical example of such a photo-fabricating process comprises forming a curable resin layer having a specified pattern by selectively irradiating with light using, for example, ultraviolet laser radiation on the surface of a liquid photo-curable material (photo-curable resin composition), according to input data in a CAD system. A further thin layer of the photo-curable resin composition is formed over this cured resin layer, and selectively irradiated to form a newly cured resin layer which is integrally laminated over the previously formed cured resin layer. This step is repeated a number of times, with or without changing the pattern in which the resin composition is irradiated to form a three-dimensional object consisting of integrally laminated multiple cured resin layers. This photo-fabricating process has been attracting considerable attention, because the target three-dimensional object can easily be prepared in a short period of time even if it has a complicated shape.
The following resin compositions (A) to (C) have been reported as the photo-curable resin composition used in the photo-fabricating process.
(A) Resin compositions containing a radically polymerizable organic compound such as urethane(meth)acrylate, oligoester(meth)acrylate, epoxy(meth)acrylate, thiol/ene compounds, photosensitive polyimide, and the like (see Japanese Patent Applications Laid-open No. 204915/1989, No. 208305/1991, and No. 160013/1989).
(B) Resin compositions containing a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro-orthoester compound, vinyl ether compound, and the like (see Japanese Patent Application Laid-open No. 213304/1989).
(C) Resin compositions containing a radically polymerizable organic compound and a cationically polymerizable organic compound (see Japanese Patent Applications Laid-open No. 28261/1990, No. 75618/1990, and No. 228413/1994).
The characteristics required of the photo-curable resin composition used for these photo-fabricating processes include a low viscosity to form a smooth liquid level and the capability of being rapidly cured by light irradiation in view of effective photo-fabrication. In addition, the cured photo-curable resin composition should be non-swelling when contacted by a photo-curable resin composition, and experience minimal deformation due to shrinkage during curing with light (i.e. in production of warped parts, indented parts, or stretched parts (overhanging parts).
Three-dimensional objects prepared by photo-fabricating methods have conventionally been used for design models and trial mechanical parts. High dimensional accuracy in accordance with the design in fine processing, mechanical strength (for example, tensile strength), toughness (for example, extensibility exhibited by tensile elongation of over 10%), heat resistance, moisture resistance, and water resistance sufficient to withstand conditions of use are especially required of these three-dimensional objects for the trial mechanical parts.
However, no conventional resin composition can satisfy the above demands. The three-dimensional objects obtained exhibit problems of deformation with the passage of time, such as production of warped parts, or indented parts, or stretched parts (overhanging parts), because of residual strain due to shrinkage during curing. These problems of deformation with the passage of time can be partly solved by the correction of the input data to the CAD system. However, the correction is insufficient to correspond to recent progress in fineness and complication in shape, and to circumstantial variations of use.
Mechanical characteristics of three-dimensional objects prepared by photo-fabrication by using conventional resin compositions containing an epoxy compound are degraded in the course of time in accordance with environmental conditions such as temperature and humidity. Therefore, use of these three-dimensional objects is unsuitable for applications requiring mechanical strength over an extended period of time.
Also, no three-dimensional object prepared by using the conventional resin compositions is provided with mechanical strength, toughness, dimensional accuracy, heat resistance, moisture resistance, water resistance, and the like required for the trial mechanical parts.
The present invention has been achieved in view of this situation and has an object of providing a novel photo-curable resin composition.
Another object of the present invention is to provide a photo-curable resin composition providing cured products which have high mechanical strength, high dimensional accuracy, and excellent toughness.
A further object of the present invention is to provide a photo-curable resin composition providing cured products with lasting minimal deformation characteristics.
A still further object of the present invention is to provide a photo-curable resin composition which can be molded to produce a three-dimensional object suitable for trial mechanical parts.
A still further object of the present invention is to provide a photo-curable resin composition which can be molded to produce a three-dimensional object which can be used under highly moisturized conditions for a long period of time.